Motion sensing apparatus, systems and techniques

ABSTRACT

A highly miniaturized electronic data acquisition system includes MEMS sensors that can be embedded onto moving device without affecting the static/dynamic motion characteristics of the device. The basic inertial magnetic motion capture (IMMCAP) module consists of a 3D printed circuit board having MEMS sensors configured to provide a tri-axial accelerometer; a tri-axial gyroscope, and a tri-axial magnetometer all in communication with analog to digital converters to convert the analog motion data to digital data for determining classic inertial measurement and change in spatial orientation (rho, theta, phi) and linear translation (x, y, z) relative to a fixed external coordinate system as well as the initial spatial orientation relative to the know relationship of the earth magnetic and gravitational fields. The data stream from the IMMCAP modules will allow the reconstruction of the time series of the 6 degrees of freedom for each rigid axis associated with each independent IMMCAP module.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims priority toU.S. patent application Ser. No. 11/059,163, filed Feb. 15, 2005, whichwas published as U.S. Publication No. US-2006-0184336-A1 andInternational Publication No. WO 2006/088863. The disclosures of theabove application and its patent publications are considered part of andare incorporated by reference in the instant application.

FIELD OF THE INVENTION

The present invention relates generally to the field of motion sensingdevices. The present invention is more particularly, though notexclusively, useful as a 6 Degree of freedom plus initial spatialorientation inertial motion measurement device for single/multiple axesapplications for use in motion capture applications. The presentinvention is also useful for proving real-time analysis and feedback toa particular motion as compared to an optimal, or predetermined, motion.

BACKGROUND OF THE INVENTION

During recent years, there has been an increasing interest in thedevelopment of sophisticated devices capable of sensing the 6 degrees offreedom motion of a single or multiple axes rigid body in 3 dimensionalspace. The devices which have been developed to sense these motioncomponents have, in the past, been rather bulky, high power, andexpensive. For instance, in order to sense angular and linear motion,both gyroscopes and accelerometers have typically been used in tandem toprovide the motion information necessary for most applications. However,these devices have been disfavored because of their bulk, high powerrequirements, and high cost.

There have been improvements in recent devices which require less power,are more precise, and slightly less bulky than prior devices. These moremodern motion sensing devices, however, are still rather bulky and as aresult, are often difficult to integrate into the device which is to bemeasured. This is particularly problematic when there is a desire tomeasure the motion of a small, lightweight device, such as a piece ofsports equipment where the addition of bulky hardware would change thenature of the movement or use of the device.

One of the earliest attempts at a miniaturized motion sensing device isdisclosed in U.S. Pat. No. 4,718,276 which issued in January of 1988 toLaughlin for an invention entitled “Angular motion sensor.” The '276patent discloses a solid electrode in the core of an angular motionsensor has a body of conductive fluid confined therein within an annularflux gap between axially spaced magnets. An arrangement of slots in thewalls of the electrode modifies the current, induced in the fluid byinertial displacement, into a circumferential component, which isinductively coupled to an output winding from which an output signal isobtained.

Attempts to decrease the physical size of motion sensing componentscontinued as presented in U.S. Pat. No. 5,831,162 which issued inNovember of 1998 to Sparks for an invention entitled “Siliconmicromachined motion sensor and method of making” discloses a method formaking and vacuum packaging a silicon micromachined motion sensor, suchas a gyroscope, at the chip level. The method involves micromachining atrench-isolated sensing element in a sensing chip, and then attaching acircuit chip to enclose the sensing element. Solder bumps serve toattach the circuit chip to the sensing chip, form a hermetic seal toenable vacuum-packaging of the sensor, and electrically interconnect thesensing chip with the circuit chip. Conductive runners formed on theenclosed surface of the circuit chip serve to electrically interconnectthe sensing element with its associated sensing structures.

The recent development of lightweight angular and linear motion sensorsinvolving MEMS components has led to innovations such as that disclosedin U.S. Pat. No. 6,504,385 which issued in January of 2003 to Hartwellfor an invention entitled “Three-axis motion sensor.” The '385 patentdiscloses a microelectromechanical system (MEMS) motion sensor fordetecting movement in three dimensions of a semiconductor waferstructure.

The MEMS device has top, middle, and bottom layers, with a movableportion, or “mover,” attached to the middle layer by a flexure thatallows the mover to move in three dimensions relative to the layers. Themover has mover electrodes that create a capacitance with counterelectrodes positioned on an adjacent layer. The capacitance changes asthe mover moves. A capacitance detector receives signals from theelectrodes and detects movement of the mover based on the change incapacitances. The MEMS device processes the detected capacitances todetermine the nature of the movement of the mover. The mover and counterelectrodes comprise x-y electrodes for detecting movement in an x-yplane parallel to the middle layer and z electrodes for detectingmovement in a direction orthogonal to the x-y plane.

While the device of the '385 patent is capable of providing measuredsignals corresponding to three axes of freedom, it nevertheless does notprovide rate information for overall motion of the device.

Continued development of MEMS sensors includes a sensor as presented inU.S. Pat. No. 6,513,380 which issued in February of 2003 to Reeds for aninvention entitled “MEMS sensor with single central anchor andmotion-limiting connection geometry.”

The '380 patent discloses a MEMS sensor including a sense element and asingle anchor that supports the sense element arranged in a centralhub-like fashion that reduces the effects of thermal stress. Usually,two or more anchors are required to suitably constrain the senseelement's motion. The anchor disclosed in the '380 patent, however,supports the sense element with connection elements having a connectiongeometry that substantially limits the motion of the sense element to asingle-degree-of-freedom.

The incorporation of MEMS sensors into motion capture devices providesfor a much lighter solution than typical motion sensors. However, thedevice of the '380 patent fails to account for the directional signalstypically provided by a gyroscope in other sensors, and thus, is notuseful as a complete motion sensor component. Further, the method ofattachment of the various MEMS components does not provide a robustsensor capable of incorporation into items being measured.

An alternative solution to motion sensing is presented in U.S. Pat. No.6,552,531 which issued in April of 2003 to Fey for an invention entitled“Method and circuit for processing signals for a motion sensor.” The'531 patent discloses a method and a circuit arrangement for processingsignals for an active motion sensor which generates at least one firstsequence of input pulses that contain motion information. By at leastone integrating filter circuit, each input pulse of a pulse train isintegrated, and an associated output pulse is generated during a periodin which the integrated signal is in excess of a predeterminable secondthreshold value after a predeterminable first threshold value has beenexceeded so that the output pulse has a time delay with respect to theinput pulse. As a result, noises of a duration which is shorter than thedelay time are effectively suppressed.

The methods for minimizing noise and improving the quality of the motioncaptured signal taught in the '531 patent make this device impracticalfor motion capture applications involving higher rates of change. Thisis particularly so given the delays which are necessarily implementedinto the sensing circuitry to improve its noise tolerance, and thus makethis device unresponsive for providing motion information for rapidlymoving items.

A more recent solution that has been proposed for measuring motion ispresented in U.S. Pat. No. 6,584,846 which issued in July of 2003 toWesselak for an invention entitled “Magnetic motion sensor.” The '846patent discloses a magnetic motion sensor, having a mobile magnet thatgenerates an essentially homogeneous magnetic field with amagnetic-field direction, and having a coupling element which isstationary within the magnetic field, and wherein a motion-dependentphysical quantity is induced in the coupling element when the magnetmoves perpendicular to the magnetic-field direction, and the inducedquantity is measured and output by a sampling element.

While the device disclosed in the '846 patent may generate amotion-based signal that is measurable, it is woefully susceptible toexternal magnetic fields. As a result, this device is not particularlyuseful in applications where the magnetic field may vary over time, ormay vary between uses.

Most recently, United States Patent Application No. 20040211258 waspublished in October of 2004 by Geen for an invention entitled “Sixdegree-of-freedom micro-machined multi-sensor.” The '258 applicationdiscloses a six degree-of-freedom micro-machined multi-sensor thatprovides 3-axes of acceleration sensing, and 3-axes of angular ratesensing, in a single multi-sensor device. The six degree-of-freedommulti-sensor device includes a first multi-sensor substructure providing2-axes of acceleration sensing and 1-axis of angular rate sensing, and asecond multi-sensor substructure providing a third axis of accelerationsensing, and second and third axes of angular rate sensing. The firstand second multi-sensor substructures are implemented on respectivesubstrates within the six degree-of-freedom multi-sensor device.

In light of the above, there is a need to provide a motion sensingapparatus and system that is capable of sensing the spatial 6 degrees offreedom and which is relatively small, lightweight, low power suitablefor portable applications, and relatively cost competitive.

SUMMARY OF THE INVENTION

What is being described is a highly miniaturized electronic dataacquisition system incorporating MEMS (Micro Electro Mechanical System)sensors that can be embedded onto moving device, such as a sportapparatus shaft, without affecting the static/dynamic motioncharacteristics of the device. Applications of the technology andapparatus of the present invention include, but are not in any waylimited to, golf clubs, baseball bats, tennis rackets, hockey sticks,etc.

In a preferred embodiment, the present invention includes a basicinertial magnetic motion capture (IMMCAP) module consisting of thefollowing sub-systems designed onto a unique highly miniaturized 3Dprinted circuit board (PCB) and includes a tri-axial MEMS accelerometer;a tri-axial MEMS rate sensor (gyroscope), a tri-axial MEMS magnetometer,Analog to Digital converter (ADC), digital to analog converter (DAC),and suitable analog signal conditioning electronics for all 9 MEMSsensors. Additionally, an embedded temperature sensor allows the sensordata to be corrected for temperature related variations in bothreal-time and post-process.

The tri-axial accelerometer and rate sensor comprise a classic inertialmeasurement unit capable of determining the change in spatialorientation (rho, theta, phi) and linear translation (x, y, z) relativeto a fixed external coordinate system. The addition of the tri-axialmagnetometer, used in conjunction with the tri-axial accelerometer,provides the capability to determine the absolute orientation of theIMMCAP, and the corresponding axis, relative to the local 1 g gravityvector and the local magnetic vector. Additionally, the magnetometeracts as a back-up rate sensor in case the rate sensors saturate due toexcessive rates of rotation or large acceleration induced gyro outputerrors.

The IMMCAP module is designed to operate under direct control of adedicated, local micro-processor (uP). Each of the nine MEMS sensorsgenerates an analog voltage that must be amplified, filtered, and offsetcorrected under the control of the local uP via the ADC, DAC, and analogsignal processing contained within the IMMCAP.

In addition to the control of the IMMCAP functions, the localmicroprocessor also formats the data stream generated by the IMMCAP fortransmission via a dedicated radio frequency (RF) digital data link.Finally, a DC-DC converter and voltage regulator provide the stablepower supply voltages needed by the analog and digital elements of theIMMCAP and microprocessor from a single primary or secondary batterycell.

Depending on the specific IMMCAP application, the associated supportelectronics may vary. In an application which is designed to capture the6 DOF of a single rigid body, i.e., golf shaft, tennis racket, baseballbat, a common format will most likely be incorporated. In someembodiments, the IMMCAP module will be an independent subsystem from therest of the support electronics in the appliance, and in others theessential components of the IMMCAP module will be integrated into asingle system with the support electronics. The digital RF data streamfrom the appliance will be transmitted via a short range ISM(industrial, scientific and medical) band transceiver to an associatedelectronics package designed to process the data stream for the specificapplication of the motion measurement system. For instance, the presentinvention can include an acoustic, optical or tactical bio-feedbacksystem for providing real-time information regarding body motionrelative to some pre-acquired motion file.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of this invention, as well as the invention itself,both as to its structure and its operation, will be best understood fromthe accompanying drawings, taken in conjunction with the accompanyingdescription, in which similar reference characters refer to similarparts, and in which:

FIG. 1 is a block diagram of a portion of the motion capture system ofthe present invention showing a basic configuration for a single axisinertial magnetic motion capture sensor array in electricalcommunication with filtering hardware and a microprocessor whichprovides a signal to a radio frequency (RF) transceiver;

FIG. 2 is a block diagram of an alternative embodiment of a portion ofthe motion capture system of the present invention showing a basicconfiguration for a multiple axes inertial magnetic motion capturesensor array in electrical communication with filtering hardware and amicroprocessor which provides a signal to a data bus for interfacingwith other motion capture sensor arrays;

FIG. 3 is a block diagram of a portion of the motion capture system ofthe present invention showing a basic configuration of multiple orsingle RF transceivers to receive data from single or multiple remotemotion capture sensor arrays for processing by a microprocessor, and forproviding data storage, and a user interface for providing control ofthe system;

FIG. 4 is a block diagram of the inertial magnetic motion capturingsensor of the present invention showing gyroscopes, accelerometers, andmagnetometers for the x, y and z axes, with the outputs of each sensorconditioned and sampled for use by the microprocessor as shown in FIGS.1 and 2;

FIG. 5 is a exemplary embodiment of the motion capturing system of thepresent invention as embodied externally and parallel to the handle ofthe shaft of a golf club, for instance, as a removable attachment to beused during training periods;

FIG. 6 is an exemplary embodiment of the motion capture system of thepresent invention as embodied internally to the handle of the shaft of agolf club, thereby providing a motion sensing club that may be used justas an ordinary club would be used with no noticeable change to the userof the club;

FIG. 7 is a diagrammatic representation of a golfer using the motioncapture system depicted in FIG. 5, and used in conjunction with thesensor elements of FIG. 1 or 2 and 3, and showing the steps for use ofthe present invention in a training mode in which the user practicesusing the device until an optimum motion is performed at which time thesystem captures the optimum motion for comparison to future motions;

FIG. 8 is a diagrammatic representation of a golfer using the motioncapture system of FIG. 7 to capture multiple motions of the motionsensor for subsequent motion analysis and comparison to known motions orother data analysis;

FIG. 9 is a flow chart representation of the “Normal Mode” of operationof the motion capture system of the present invention beginning with theinitialization of the shaft microprocessor, initialization of the motiondata controller and progression to data acquisition mode, or to standbymode;

FIG. 10 is a flow chart representation of the “Real Time” dataacquisition mode of the motion capture system of the present inventionshowing the acquisition of motion data and comparison to stored motiondata in order to provide a real-time feedback signal to the user, andrelaying this real-time motion data to the controller for subsequentanalysis or comparison to known motion data;

FIG. 11 is a flow chart representation of the “Post Processing” dataacquisition mode of the motion capture system of the present inventionshowing the capturing of motion data in a circular buffer until an eventtrigger is sensed, resulting in the cessation of the motion datacapturing and formatting of the data for transmission to a PC or PDA forsubsequent analysis;

FIG. 12 is a block diagram showing the component location and relativeconstruction for an exemplary inertial magnetic motion capture (IMMCAP)module as used in the present invention; and

FIG. 13 is a multiple IMMCAP module system on a human body, with 3modules per limb plus 4 for the spin/head resulting in a total of 16modules, through which the entire skeletal motion can be capture forgait analysis, special effects, or sport training applications.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In a preferred embodiment, one motion capturing system of the presentinvention includes a motion sensing module, and microprocessorcontrolled interfaces which capture the motion data and analyze the datafor real-time feedback, or for post-processing analysis. As will bediscussed further below, there are numerous applications of the motioncapture system of the present invention. However, in order to discussthese various applications, a basic discussion of the hardware of thepresent invention is provided.

Referring initially to FIG. 1, a block diagram of a portion of themotion capture system of the present invention is shown and generallydesignated 100. Motion capture system 100 includes an inertial magneticmotion capture system (IMMCAP) module 102 in electrical connection witha microprocessor 104 which provides control signals to the module 102,and receives status information from the module 102 to facilitate properoperation. Analog output signals generated within the IMMCAP module 102are internally converted to 12 bit digital representations via animbedded analog to digital converter (ADC). The digitized signals fromthe module 102 are relayed through microprocessor 104 to RF transceiver108 for transmission to a remote receiver (not shown in this Figure). Apair of low drop out voltage regulators 106 and 110 provides a constantvoltage supply from DC-DC converter 112 and battery 114 to optimizebattery life and reduce the noise generated by the DC-DC converter 112.

As an alternative to the motion capture system shown in FIG. 1, amulti-sensor system is presented in conjunction with FIG. 2. Morespecifically, FIG. 2 is a block diagram of an alternative embodiment ofa portion of the motion capture system of the present invention andgenerally designated 140. Motion capture system 140 includes an IMMCAPmodule 102 in electrical connection with a microprocessor 120. The datafrom the module 102 is processed by microprocessor 120 and placed on adata exchange bus 122. In a preferred embodiment wherein there aremultiple modules 102 and microprocessors 120, data from these multipledevices may be easily exchanged over the data bus 122.

A master microprocessor 124 receives data from data bus 122 for storagein a local memory 125, and/or for transmission via RF link 126 to areceiver (not shown this Figure). For portable applications, a battery128 provides a voltage to DC-DC converter 130 which in turn providespower to motion capture system 140. Additional low drop out regulators106 may be incorporated to ensure low noise and stable voltage levelswhich can be particularly important to minimize sensing errors in themodule 102.

Referring now to FIG. 3, a block diagram of a receiver portion of themotion capture system of the present invention is shown and generallydesignated 200. Receiver portion 200 includes a basic configuration of amicroprocessor 202 in connection with multi-channel capable (multiple)RF transceivers 204 and 206 to receive RF data from remote motioncapture sensor arrays 100 and 140, for example, for processing bymicroprocessor 202.

A user interface 208 is provided for control of the motion capturesystem, and may include an LCD display 210 and a data input device 212,such as a keypad or keyboard, for instance. A data bank 213 is providedto microprocessor 202 and may include a memory, such as a circularmemory buffer, which receives motion data from one or more IMMCAPmodules 102, for storage and later retrieval and analysis. Also, apermanent memory 216, such as FLASH memory may be provided for storageof motion capture data, or for storage of predetermined or optimummotion data for analysis and/or comparison.

Module 102 is shown in FIG. 4 as a block diagram of the inertialmagnetic motion capturing (IMMCAP) sensor of the present invention.Module 102 includes an orientation sensing gyroscope array, such asx-axis gyroscope 302, a y-axis gyroscope 304, a z-axis gyroscope 306. Inaddition, X, Y and Z axis accelerometers 308 and 310 are also provided.Magnetometers 312 and 314 for the X, Y and Z axes are also provided. Theoutputs of these sensors are conditioned with analog signal conditioninghardware 322, 324, 326, 328, 330, 332, 334, 336 and 338. The outputs ofthese signal conditioners are fed into an analog to digital converter320 which in turn is routed to microprocessor 104 (as shown in FIGS. 1and 2).

A magnetic offset correction digital to analog converter 316 may beprovided, along with a magnetic polarity self test circuit 318 in orderto minimize the effect of magnetic sensor and signal conditioning offseterrors (dynamic magnetic fields) on the overall accuracy of the IMMCAPmodule.

As a preferred embodiment, FIG. 5 presents an exemplary embodiment ofthe motion capturing system of the present invention on a golf club, andgenerally designated 400. Motion capturing system 400 includes a shaft402 having a shaft grip, or handle, 404 and a motion sensor 406 mountedalongside the handle 404 of the shaft 402 of a golf club. As shown, apair of removable attachment clips 408 and 410 may be used duringtraining periods to secure the motion sensor 406 to shaft 402. Whentraining period is finished, the sensor 406 may be easily removed fromshaft 402, thereby returning the club to its ordinary state.

As an alternative embodiment, FIG. 6 depicts another exemplaryembodiment of the motion capture system of the present inventiongenerally designated 440. As shown, motion capture system 440 includes ashaft 442 formed with a grip 444. An internal IMMCAP module 446 is sizedto be received within the shaft 442 through cap 448 and may be equippedwith an ON-OFF switch 450. Because the module 446 is neatly concealedwithin the shaft 442, the use of the club is uninhibited therebyproviding for a functionally equivalent club for practice and motioncapturing purposes. This is particularly advantageous because thegolfer, in this instance, may handle the club as if it were un-modified,thereby allowing the most accurate motion capturing to occur.

Referring now to FIG. 7, a diagrammatic representation of a golfer usingthe motion capture system depicted in FIG. 5 is shown. Specifically,golfer 500 is shown using a golf club 502 equipped with an IMMCAP module504. Module 504 measures motion data from the club including the sixdegrees of freedom, and relays this information to controller 508(either through a wired connection, or) through a wireless connectionwith antenna 510. This data is then displayed on the controller for thegolfer 500, or it may be analyzed and compared to a known, or optimizedmotion.

It is to be appreciated that the motion capture system of the presentinvention may be used in conjunction with the sensor elements of FIG. 1or 2 and 3. As shown in FIG. 7, a headset 512 may be provided to golfer500 to provide an audible feedback signal. This feedback signal may bereceived via a hardwired or RF link from controller 508 based upon amotion data analysis and comparison to a known, optimized, or selectedmotion.

FIG. 7 also lists steps 1-5 for the use of the present invention in atraining mode in which the user practices using the device until anoptimum motion is performed at which time the system captures theoptimum motion for comparison to future motions.

Referring now to FIG. 8, a diagrammatic representation of a golfer 500using the motion capture system of FIG. 7 to capture multiple motions isshown. The motion sensor 504 is attached to club 502 while being movedby golfer 500 and motion data is captured and transmitted via RF signalto antenna 510 of controller 508. This motion data is received andstored for subsequent motion analysis and comparison to known motions orother data analysis. As shown, this motion data may be transmitted fromcontroller 508 to a PDA 530 or PC computer 532 through antennae 534 and536, respectively.

The motion data that is received by controller 508 may be stored forfuture retrieval, or may be analyzed in real time to provide the golfer500 real-time feedback as to the errors in his motion, or deviations inhis motion from a known, desired or optimal, motion. Also shown in FIG.8 are the steps 1-2 for archiving motion data captured from module 504.This data may also be transmitted from controller 508 to PDA 530 and PC532 via a wired interface as shown in dashed lines, such as an RS232 orUSB interface.

FIG. 9 is a flow chart 600, representing the “Normal Mode” of operationof the motion capture system of the present invention. The flow chartbegins in step 602 with the manual turning on of the shaftmicroprocessor. Once on, in step 604, the initialization of the shaftmicroprocessor begins, followed by initialization of the IMMCAP modulein step 606. Once on and stable, the microprocessor sends a command tothe IMMCAP module in step 608 to begin sampling IMMCAP data, temperaturedata, and other sensor data for a self-check of the system.

Once the self check is completed, in step 610, the microprocessor beginsclocking the sensor data for conversion by the ADC converter in step612. Once sampled, the motion data is transmitted to the controller instep 614. If an operating mode update is requested by the shaftprocessor, once every 10 transmissions, in 504, a response is receivedin step 616, and the operating mode is updated in step 618. If thesystem is in the normal mode, data sampling continues at 100 msintervals as shown in step 620, otherwise, the system is placed in a lowpower stand-by mode with a low speed sample rate of 1500 milliseconds,with control returning to step 608 where the system re-checks the IMMCAPdata outputs at the 1500 millisecond sample rate.

Referring to FIG. 10, a flow chart representation of the “Real Time”data acquisition mode of the motion capture system of the presentinvention is shown and generally designated 650. Process 650 begins withstep 652 with a manual turn-on of the controller and microprocessor, andcontinues with system initialization in step 654. Once initialized, thesystem awaits receipt of the shaft motion data, such as an RF datapacket, in step 656.

Once the data packet is received in step 656, the data is analyzed andparsed for establishing sensor-related program variables to be used inthe subsequent analysis of motion data. In order to provide real-timefeedback in this mode, the real-time sensor data stream must be timesynchronized with the stored reference motion file. Once synchronizationis achieved in 660 and verified in 662, the processor now receives timesynchronized real-time data from the motion sensors.

As real-time data is received from motion sensors, the known timesynchronized motion data is synchronized and compared to reference dataand a motion error is calculated in step 666. The amplitude of thiserror signal from step 666 may be greater than a predetermined erroramplitude, thereby providing an error signal, such as an audible errortone, in step 668. This error signal may be transmitted to a user'sheadset via an RF link or hardwired to provide immediate and specificerror information regarding the current motion or motions. The errorfeedback may be terminated following the end of the reference data instep 672, and the system may reset itself in step 674 to await the nextmotion sequence.

In a preferred embodiment of the system of the present invention, theacquisition of motion data and comparison to stored motion data may beaccomplished in real time, thereby giving immediate feedback to theuser. Alternatively, this data may be captured and analyzed later in apost-processing analysis.

For example, FIG. 11 includes a flow chart representation of the “PostProcessing” data acquisition mode and is generally designated 700.Process 700 begins with step 702 in which the controller is manuallyturned on, and the system is initialized in step 704. Once initialized,the controller awaits receipt of an RF data packet from the shaft modulein step 706. The data from the shaft module is then analyzed and parsedand stored in a circular buffer in step 708.

The motion file capture is terminated by the detection of apre-determined data signature of a ball strike, indicating theend-of-record for the particular event in step 710. If no trigger eventoccurred, the process returns to step 706 to await the next data packetto be stored in the sequential circular buffer. On the other hand, ifthe trigger event occurred, motion data is transferred from the EEPROMdata to flash memory in step 714 for more permanent storage for lateranalysis.

The motion capture system of the present invention may provide themotion data in EEPROM for exchange via RF or USB transfer to a PC or PDAfor analysis and perhaps graphical display in step 716 to further assistthe golfer in his quest for a perfect swing.

Referring now to FIG. 12, a block diagram showing the component locationand relative construction for an exemplary inertial magnetic motioncapture (IMMCAP) module as used in the present invention is shown andgenerally designated 900. IMMCAP module 900 may include threemagnetometers 902, 904 and 906, three accelerometers 908, 910, and 912,and three gyroscopes 914, 916 and 918. It will be further discussedbelow that in certain circumstances, the inclusion of gyroscopes 914,916 and 918 to the present invention may be unnecessary.

In a preferred embodiment, module 900 may be formed on a flexiblecircuit board thereby providing for the manufacturing of the module in aflat, planar configuration, with the sides of the module being formedinto a cube after assembly. This will significantly simplify themanufacturing costs and minimize manufacturing challenges that wouldresult from a multi-circuit board cube assembled to form the required3D, orthogonal orientation of the X, Y, Z axis sensors. This is not tosuggest, however, that the multi-circuit board cube is not a suitablesolution to the challenges solved by the present invention. As futureintegration technology will allow all three orthogonal axes to beincluded on a single IC package, the 3D printed circuit boardrequirements for the present embodiment will become relaxed.

A MEMS Sensor Based Full-Body Motion Capture System

As an alternative embodiment of the present invention, a highlyminiaturized electronic data acquisition system is contemplated andcapable of measuring and recording the spatial orientation andtranslation, 6 degrees of freedom (DOF), of each independent bodysegment through 3D space in real-time. Knowing the 6 DOF of each bodysegment together with the known relation of the body segments, areconstruction of the entire body motion in 3D space via a computergenerated representation of the subject under study is possible. Thepotential application of such a system range from sports rehab motionanalysis to movie special effects and animation.

The system incorporates multiple IMMCAP modules as described in FIG. 1.The IMMCAP modules will be networked to a single control processormodule (CPM) that will coordinate, process, and store the data outputfrom the IMU array for immediate transfer via RF/IR link or for laterdownload and analysis as described in FIG. 2. The IMMCAP/CPM modulearray will be integrated into a highly compliant body-suit with eachIMMCAP module assigned and mounted to a rigid body segment, i.e. head,upper arm, forearm, etc., requiring a single CPM module andapproximately 16-20 IMMCAP modules to monitor the entire set of bodyaxes.

FIG. 2 represents the block diagram of the system design. The single CPMmodule is located in the general area of the lower back with each of the16-20 IMMCAP modules secured to their respective body segment. Thesystem is networked via a one wire half duplex, or two wire full duplex,local area network (LAN) embedded into the body-suit. The CPM modulewill provide power, by additional wires, and communication control forall IMMCAPs via the LAN.

The block diagram of the CPM module is shown as part of FIG. 2. Thefigure illustrates the subsystems incorporated into the CPM modulesconsisting of:

-   -   1) Battery Pack    -   2) DC-DC converter    -   3) Microprocessor    -   4) Non-volatile memory    -   5) RF/IR/hardwire full/half duplex serial data link (optional)

The battery pack consists of 1 to 3 primary or secondary cells toprovide system power. The DC-DC converter provides the operating DCvoltage to operate the CPM module and provides the distributed power tothe IMMCAP modules via the communication/power LAN. The microprocessorin the CPM runs the control software to synchronize the data acquisitionand transfer from the IMMCAP modules to the CPM. Additionally, theprocessor formats the data for local storage in non-volatile memory andimmediate or delayed data downloading via the hard wire connection orRF/IR data link. The CMP components are selected for low power operationto effect maximum operating time for a given battery capacity.

The block diagram of the IMMCAP modules is shown in FIG. 4. The figureillustrates the subsystems incorporated into the IMMCAP modulesconsisting of:

-   -   1) Tri-axial MEMS accelerometer    -   2) Tri-axial MEMS rate sensor (gyroscope)    -   3) Tri-axial MEMS magnetometer    -   4) Temperature sensor    -   5) Micro-controller    -   6) Analog to Digital converter (ADC)    -   7) Digital to Analog converter (DAC)    -   8) Analog signal conditioning electronics for all 9 MEMS sensors

The tri-axial accelerometer and rate sensor comprise a classic inertialmeasurement unit (IMU) capable of determining the change in spatialorientation (rho, theta, phi) and linear translation (x, y, z) relativeto a fixed external coordinate system. The addition of the tri-axialmagnetometer provides the capability to determine the absoluteorientation of the IMU, and the corresponding body axis, relative tomagnetic north to provide an absolute orientation. Additionally, themagnetometer acts as a back-up rate sensor in case the rate sensorssaturate due to excessive rates of rotation.

Each of the nine MEMS sensors generates an analog voltage that must beamplified, filtered, and offset corrected under control of the localmicro-controller via the ADC, DAC, and analog signal processing.Additionally the micro-controller also interfaces with the CPM modulevia the LAN to execute commands issued by the CPM and for data transferto the CPM. Finally, the DC-DC converter and voltage regulator, locatedin the support electronics, provide the stable power supply voltagesneeded by the analog and digital elements of the IMMCAP from the DCvoltage supply associated with the LAN.

Inertial-Magnetic Motion Capture (IMMCAP) Sensor Array for Single andMultiple Axes Motion Capture Applications

GENERAL DESCRIPTION AND APPLICATIONS

As another alternative embodiment of the present invention, a highlyminiaturized, wireless electronic data acquisition system is disclosedand is capable of measuring and recording the spatial orientation andtranslation, 6 degrees of freedom (DOF), of single and multiple rigidaxes through 3D space in real-time. Additionally, the initial spatialorientation can also be determined referenced to the earths' terrestrialgravity and magnetic fields.

Although an IMMCAP based motion capture system is applicable to almostany sports activity, gait/motion analysis, motion picture specialeffects, or virtual reality application, the IMMCAP system will bedescribed within the context of golf swing application for the sake ofthis discussion.

The golf industry application of the IMMCAP technology ranges from thereal-time capture of the motion of a golf swing for analysis,biofeedback training, or club fitting to the capture of the entire bodymotion using multiple IMMCAP sensors. The primary advantage of an IMMCAPenabled system, in addition to the extremely high degree of accuracyprovided, is that the motion capture process does NOT require the golferto be placed in an unnatural environment. An IMMCAP system allows thegolfer to practice/play in a normal situation of his/her choice, i.e.golf course, practice putting green, or driving range, withoutrestriction. By allowing the swing/motion to be performed under naturaland varying conditions, a more representative and realistic sense of theswing dynamics will be measured.

Current video based systems require the golfer to be placed in an“unnatural” studio environment to allow multiple cameras to view theswing path within a highly restricted spatial volume. Similarly, largestationary swing analysis systems require the golfer to be “tethered” tothe system at a single point.

The IMMCAP sensor array module is comprised of multiple, highlyminiaturized MEMS (Micro Electro Mechanical System) sensor elements thatallow the 3D motion of the sensor, and thus the rigid body which it isattached, to be captured and recorded in real-time. The IMMCAP sensorcan be integrated into a complete system depending on the application.

What follows is a brief description of unique applications of the IMMCAPmodule for use within the golf industry.

Putting Trainer and Swing Analysis:

This system is designed to capture the complete swing dynamics of a golfswing and provide real-time acoustic feedback to allow a golfer topractice a particular swing path to create the required “muscle memory”of the desired stroke. Prior to beginning the practice session, apreviously saved reference swing path is used to compare the currentswing path in real-time. This reference swing can be determined andsaved by the golfer or by a coach to be used in the current trainingsession and recalled at a later time to become the reference swing ifdesired. As the golfer practices the swing path, the current swing pathis compared to the reference. If the current swing path deviates fromthe reference path, an acoustic tone is generated at the instant thepath diverges from the reference with the tone increasing in intensityas the swing error becomes larger. If the golfer can execute the swingWITHOUT generating any tone, the current swing path is identical to thereference. The following swing parameters can be used as the trainingtarget OR used in any combination:

a) tempo

b) swing path

c) face angle

d) heel-toe angle

e) loft angle

f) aim point

System sensitivity is adjustable to allow the golfer to modify the grosserrors in the swing consistency then increasing the sensitivity ashe/she improves. Ultimately the golfer should be able to consistentlyexecute the swing without the need for the acoustic feedback once themuscle memory has been reinforced.

An alternative to the acoustic tone feedback directly to the golfer is agraphical error representation on a hand-held device, Palm Pilot or PDA,used in the context of a coaching environment. Swing improvements basedon the analysis of the current swing path can be entered by the coachfor the student to execute without the need for the coach to bephysically present once the new swing “reference” has been downloaded tothe system via a wireless link. This wireless link also enables thesystem to be Internet enabled allowing data to be up/down loaded from apay-per-use or fee based training website.

The system of the present invention is a three to four piece systemwhich may, depending on the configuration, consist of the following:

-   -   1) Shaft mounted wireless appliance incorporating an IMMCAP        module.    -   2) Belt mounted wireless control/display/digital signal        processing (DSP)    -   3) Wireless headset for error tone generation/acoustic        bio-feedback    -   4) Optional wireless PDA software application for coaching input        and swing modification.

The shaft mounted appliance containing the IMMCAP plus associatedsupport electronics, i.e. power supply, wireless data link,microprocessor, is the size of an AA battery and weights approximately10 grams. Once in mass production, all the system components,particularly the shaft mounted sub-system, can be greatly miniaturizedover the already small current size/weight.

This system is capable of being applied to any type of golf club/swingtraining application, i.e. irons and woods, but the acoustic feedbackfeature would not be appropriate due to the fast swing dynamics. Avisual feedback system using the aforementioned PDA display would beutilized by the golfer and/or coach.

Club Fitting:

The current state of club fitting is quite primitive due to the lack ofany consistent swing dynamics measurement capability in an ordinarypro-shop. An IMMCAP based system has been developed that can beinstalled INSIDE a club shaft near the top of the shaft. The system isdesigned to record the 3D dynamics of up to hundreds of club swingswhile the golfer uses the club in the normal fashion, i.e. either anormal round of golf or at a driving/putting range.

By recording a large number of swing events representing the golf swingin a varied environment and conditions, a better estimate of thegolfers' average performance can be determined. This information willallow a club fit that best serves the golfer over the entire gameinstead of depending on a single swing set in an unnatural environmentto determine the proper club fit. The current system allows the strokedata to be downloaded to an application software package running on thepro-shop computer or to be downloaded via the Internet for analysis andfit recommendations from a remote site. This capability also allows thetest club to be sent to a prospective client not near a pro-shop forremote fitting.

Currently the present invention may be placed within the shaft but couldbe configured as an external device attached to the external shaft.

Full Body Motion Analysis:

In addition to the 3D club motion dynamics, an entire body suitincorporating multiple IMMCAP modules allow the entire body motion to becaptured for analysis. By looking at the entire body/club system withthe detail offered by the IMMCAP modules, Golf body mechanics trainingcan be redefined.

Theory of Operation

The basic IMMCAP module consisting of the following sub-systems designedonto a unique highly miniaturized 3D printed circuit board (PCB):

1) Tri-axial MEMS accelerometer

2) Tri-axial MEMS rate sensor (gyroscope)

3) Tri-axial MEMS magnetometer

4) Temperature sensor

5) Analog to Digital converter (ADC)

6) Digital to Analog converter (DAC)

7) Analog signal conditioning electronics for all 9 MEMS sensors

The tri-axial accelerometer and rate sensor comprise a classic inertialmeasurement unit capable of determining the change in spatialorientation (rho, theta, phi) and linear translation (x, y, z) relativeto a fixed external coordinate system.

The addition of the tri-axial magnetometer, used in conjunction with thetri-axial accelerometer, provides the capability to determine theabsolute orientation of the IMMCAP, and the corresponding axis, relativeto the local 1 g gravity vector and the local magnetic vector.Additionally, the magnetometer acts as a back-up rate sensor in case therate sensors saturate due to excessive rates of rotation. Finally, theembedded temperature sensor allow for temperature induced driftcompensation in both real-time and post-processing.

The IMMCAP module is designed to operate under direct control of adedicated, local micro-processor (uP). Each of the nine MEMS sensorsgenerates an analog voltage that must be amplified, filtered, and offsetcorrected under the control of the local uP via the ADC, DAC, and analogsignal processing contained within the IMMCAP.

In addition to the control of the IMMCAP functions, the local uP alsoformats the data stream generated by the IMMCAP for transmission via adedicated radio frequency (RF) digital data link. Finally, a DC-DCconverter and voltage regulator provide the stable power supply voltagesneeded by the analog and digital elements of the IMMCAP and uP from asingle primary or secondary battery cell.

Depending on the specific IMMCAP application, the associated supportelectronics will vary. In an application which is designed to capturethe 6 DOF of a single rigid body, i.e., golf shaft, tennis racket,baseball bat, a common format will most likely be incorporate. A lowmass appliance attached to the rigid body may consist of the following:

1) basic IMMCAP module

2) uP

3) Rf data link

4) DC-DC converter/battery

In some embodiments, the IMMCAP module will be an independent subsystemfrom the rest of the support electronics in the appliance, and in othersthe essential components of the IMMCAP module will be integrated into asingle system with the support electronics.

The digital RF data stream from the appliance will be transmitted via ashort range ISM band transceiver to an associated electronics packagedesigned to process the data stream for the specific application. Anexample, but not limited to, would be an acoustic bio-feedback system asdescribed above.

Inertial-Magnetic MEMS Based Sensor System for Single and MultipleSegment Motion Capture Systems

A highly miniaturized multi-sensor module of the present inventionconsists of inertial and magnetic sensor subsystems capable of sensingthe absolute orientation and motion of a rigid body relative to anexternal reference coordinate system in-situ.

The intended application for this sensor system is to capture thereal-time absolute motion of a single rigid body, i.e. golf shaft orbaseball bat, or multiple rigid bodies, i.e. multiple human bodysegments, for immediate of post-event analysis and display.

Current motion capture systems fall into two distinct groups. The 1^(st)relies on multiple spatially calibrated cameras to record the motion ofreference points on one or more rigid bodies of interest onto video tapefor post-processing. This video post-processing is capable of extractinga subset of the six degrees of freedom, (DOF) but not all. An example ofa non-observable DOF would be the rotation of the lower arm segmentabout the long axis or rotation of a golf club about the shaft axis

The 2^(nd) type incorporates a local, 3 meters or less, pulsed magnetic“beacon” with magnetic sensors attached to the rigid bodies. Althoughthis system can extract all 6 DOF, the magnetic sensors and supportingelectronics/cables are quite large lending itself more to real-timemotion animation then motion capture.

The Inertial-Magnetic Motion Capture system (IMMCAP) described here isunique to both of the aforementioned systems in that it usesconventional inertial motion measurement concepts in conjunction withboth the earth gravity and magnetic fields to describe the 6 DOF ofsingle or multiple rigid bodies relative to an external frame ofreference.

Conventional inertial measurement units (IMU) incorporate three axes oforthogonal accelerometers and three axes of gyroscope to fully sense the6 DOF. The IMU outputs the linear translations, X, Y, and Z motion inspace, as well as the three rotation angles, roll, pitch, and yaw.Unfortunately, theses 6 DOF are relative to a PRE-KNOWN initial startingposition/orientation and cannot yield an absolute position/orientationother then referenced to the initial position.

In the IMMCAP system, this problem is partially overcome by utilizingthe outputs of the three axis accelerometer together with threeadditional axes of magnetometer. If the rigid body is known to bemotionless, for as little as 1 msec, this sensor combination acts as anorientation sensor yielding an absolute orientation of the rigid bodyrelative to the earth gravity/magnetic field. These fields have a stableand known orientation relative to each other as well as to any arbitraryexternal frame of reference. With this initial orientation known, theabsolute orientation can be determined via the IMU. As the initialorientation is usually adequate for motion capture, the absolute initialtranslation can also be obtained by placing the single or multipleIMMCAP modules at know absolute X, Y, Z positions relative to anexternal reference to obtain absolute position and orientation.

The typical IMMCAP module is comprised of the following sub-systems:

-   -   1) tri-axial MEMS accelerometer    -   2) tri-axial MEMS gyroscope    -   3) tri-axial MEMS magnetometer    -   4) temperature sensor    -   5) analog signal conditioning for MEMS sensor array    -   6) analog to digital converter (ADC) for MEMS output    -   7) analog voltage conditioning    -   8) RF interface for data/control input/output (optional if        external)    -   9) embedded micro-processor (optional if external)    -   10) micro battery (optional if external)

The IMMCAP module, comprising sub-systems 1-6, has been produced withoff the shelf components in a package size of 0.7″ (18 mm)×0.3″ (8mm)×0.4″ (10 mm). The modules can be significantly reduced in size viathe use of application specific integrated circuits (ASIC) and/or dielevel multi-chip modules (MCM).

Two exemplary embodiments of the present invention are described belowwith many obvious derivatives also possible and fully contemplatedwithout departing from the spirit of the present invention.

Golf Swing Motion Capture.

By integrating the IMMCAP module with sub-systems 7-9, a self powered,wireless single axis motion capture unit can be realized for a golf clubshaft. Due to extreme small size and weight possible utilizing the MEMSsensor technology, the motion capture unit can be directly attached tothe golf shaft, just under the grip area to minimize the rotating mass.An appropriate sample rate of the sensor signals will be based on theNyquist criteria and the frequency content of the action to be measured.The scanned sensor outputs will be digitized and transmitted via an RFinterface to an external electronic unit used either for real-timebio-feedback muscle training purposes and/or to be stored forpost-analysis. By storing an absolute or relative stroke reference incomputer memory, each stroke event can be compared to the reference todetect deviations in the following relative to the reference:

-   -   1) initial face angle    -   2) face angle as a function of time or back stroke angle    -   3) toe-heel angle as a function of time or back stroke angle    -   4) head speed as a function of time or back stroke angle    -   5) loft angle at the point of ball impact    -   6) entire 6 DOF stroke dynamics from stroke start to ball strike

This information can be utilized in real-time as a bio-feedback signalfor muscle memory and/or for post analysis of the event.

Full Body Motion Capture.

By attaching multiple IMMCAP modules onto the human body, 3 modules perlimb plus 4 for the spin/head resulting in a total of 16 modules, theentire skeletal motion can be capture for gait analysis, specialeffects, or sport training applications. Each IMMCAP module would becoupled to an “intelligent node” integrated into a highly flexible bodysuit. The 16 nodes would be networked to a central control unit via anembedded four wire power/data bus also integrated into the body suit.The central control unit would provide synchronization, power, andexternal interface for the IMMCAP data stream.

The data collected in this system may be telemetry-linked to a basestation capable of receiving the motion capture data for in-situevaluation, post measurement analysis, or a combination of both in-situand post measurement analysis. This telemetry may be through RFtransceivers as described above, or through optical transmission such asthrough an infrared data link, as is known in the art.

High Rate Applications

By utilizing both the MEMS gyro and the magnetometer for body rotationdetection, the shortcomings of each sensor can be partially or totallycompensated.

Gyro Limitations for the Determination of Angular Rotation:

All solid state gyros generate a voltage output that is proportional tothe rotational velocity ω in mV/degrees/sec. This requires that thetotal rotation about an axis from a time t=0 to t=T be obtained byintegrating the gyro signal such that

$\begin{matrix}{{\Theta(T)} = {\int_{0}^{T}{{\omega_{gyro}(t)}\ {\mathbb{d}t}}}} & (1)\end{matrix}$

The ω_(gyro) (t) signal is comprised of the following superimposedsignals shown asω_(gyro)(t)=(ω_(signal)(t)±ω_(noise)(t))+(ω_(o)±ω_(oerror))  (2)

where ω_(signal)(t) is the true signal generated in response to therotation, ω_(noise)(t) is the random component of the signal due to thepresence of in-band random noise present in all linear signals, ω_(o) isthe zero rotation value from the sensor, and ω_(oerror) represents theinstantaneous value of ω_(noise)(t) at t=0 when ω_(o) was determined.Rearranging (2) to represent the actual signal due to rotation yieldsω_(signal)(t)=(ω_(gyro)(t)−ω_(o)±ω_(oerror)(t=0))±ω_(noise)(t)  (3)

substituting (3) into (1) and assuming the ω_(noise)(t) will integrateto zero yielding the simple resultΘ_(calc)(T)=Θ_(actual)(T)±Tω _(oerror)(t=0)  (4)

The above implies that the uncertainty in the calculated rotation asmeasured by the gyro increases with time which limits the useful timethe sensor output is usable based on a desired angular accuracy. Theω_(oerror) value can be reduced by limiting the signal bandwidth and byaveraging multiple measurements of ω_(o) over some time interval whenthe rotation is known to be zero but this averaging time is limited dueto practical application.

The second and more serious limitation of the current generation of MEMSgyros is the limited sensor dynamic range. Currently, the practicalupper limit for MEMS gyros is of the order of 1200°/sec which isinsufficient for some motion capture applications, i.e. theinstantaneous angular velocity of the lower arm of a baseball pitcherwill easily exceed this limit under some circumstances. This upper limitcan be further increased by special electronic means but with anassociated reduction of the low rate sensitivity due to the limiteddynamic range of the MEMS gyro.

In summary, it is to be appreciated that MEMS and gyroscope limitationscan be overcome by using the magnetometer as the primary rate sensorwith the gyros taking the role of an ancillary rate sensor channel.

Magnetometer Based Angular Rate Sensor

In one embodiment of the present invention, there is an applicationusing just the tri-axial accelerometer and tri-axial magnetometerwithout the need for the tri-axial gyros. More specifically, if it isassumed that the local magnetic field is constant over the extent of thespatial volume, the magnetometer can act as a differential gyro. Thisallows the mag/accel combo to act like a standard accel/gyro inertialsensor in addition to the combo providing the initial start orientation.The only caveat is there is a singularity when the magnetic field isco-axial with one of the mag axes resulting in no magnetic component inthe plane normal to the axes. This may not be a problem in mostapplications and can greatly reduce cost, size and power requirementsbut eliminating the 3 relatively large gyros.

The IMMCAP magnetometer is primarily used in conjunction with theaccelerometers to determine the initial spatial orientation of the bodyin space. If it is known that the body is not accelerating in any axis,the accelerometer becomes a gravitometer allowing the body orientationto be determined relative to the earth gravity field. The magnetometerdetermines the body orientation relative to the earth magnetic field.Combining this information allows determination of the absolute spatialorientation relative to the two external fields. Importantly, it must beassumed that there is no ferromagnetic material local to themagnetometer to avoid field distortion and subsequent orientationerrors.

In addition to the above role, the magnetometer can act as adifferential rate sensor in all three axes. The rotation about the Zaxis can be deduced by observing the rotation of the magnetic fieldvector in the X-Y plane. In a time sampled system, as is the IMMCAPapplication, the angle of the B_(XY) magnetic field vector is determinedfor the Nth sample asΘ_(ZN)=tan⁻¹(B _(XN) /B _(YN))  (5)

where Θ_(ZN) is the angle of the B_(XY) vector component relative to theX axis.

The next sample yieldsΘ_(Z(N+1))=tan⁻¹(B _(X(N+1)) /B _(Y(N+1)))  (6)

the angular velocity about the Z axis is determined by the followingω_(Z)=(Θ_(Z(N+1))−Θ_(ZN))/T _(sample)  (7)

where ω_(Z) represents the average angular velocity over the time fromsample N to N+1. Of course, ω_(X) and ω_(Y) are found in a similar way.Again due to system noise the actual angular velocity will berepresented asω_(N)=ω_(Ncalc)±ω_(Nnoise)  (8)

To determine the total rotation about an axis, the signal is integratedover a time T resulting inΘ(T)=T(Σω_(N)±Σω_(Nnoise))  (9)

Due to the noise being random and averages to zero, the above results inΘ(T)=T Σω _(N)  (10)

A very important result is the lack of an integrated error term as foundin eqn. (10) due to the magnetometer representing the rotationalvelocity as a rate of change, or differential signal, unlike the gyro.

This implies that the magnetometer rate sensor can be used indefinitelywithout loss of accuracy. Equally important, there are no dynamic rangeissues associated with using magnetometers as rotation rate sensorsunlike the gyro. The dynamic range of the magnetometer rate sensor isdetermined by the sensor bandwidth, rate of change from sample N to N+1,unlike the gyro which is related to the sensor gain. The usablebandwidth of the magnetometer is in excess of 25 Mhz, which equates to aridiculously high rotation rate never to be experienced by a human bodysegment.

There are two downsides with the magnetometer rate sensor. The 1^(st) isa mathematical singularity. If the external earth magnetic field isaligned with any of the sensor axes, the rotation rate about that axiscannot be determined. As an example, if the earth field is aligned withthe Z axis, there is no magnetic field component projected onto the X-Yplane obviously precluding the calculation of the arc tan.

This can be dealt with in two ways. It is a simple task to determine ifindeed the singularity exists, i.e. X and Y components measure to bezero. If so determined, the 1^(st) solution is to revert to the MEMSgyro for Z axis angular rotation data, IF it is available AND therotation rate does not exceed the dynamic range of the sensor aspreviously discussed. Since the gyro data will be used for a short time,i.e. until the singularity is gone, the aforementioned erroraccumulation due to ω_(oerror) will be negligible.

The 2^(nd) solution is to extrapolate thru the singularity by keeping Nprevious samples in a FIFO buffer. If the singularity is determined toexist, the N samples can be used as input to a medium to high orderpolynomial to estimate the lost data until the singularity is gone. Thisis reasonable given the unlikely probability the singularity will existfor more then a few sequential samples given the dynamic nature of themotion.

A 2^(nd) possible problem associated with the magnetometer rate sensoris the sensitivity to external field distortions. If the fielddistortions cause an unequal change in the two vector components, i.e.if the X and Y vector components are not changed by the same fractionvia the distortion source for Z axis rotation measurements, an error inthe calculated Z axis rotation will likely result. The severity of thiseffect is most likely highly case specific and will not be addressedhere.

Regardless of the severity, this distortion condition is easily detectedby the fact that any distortion will ALWAYS be accompanied by change inthe TOTAL vector magnitude. Any external ferromagnetic material will notonly cause distortion in the individual vector components but also causethe local field strength, or vector sum of the components, to exceed thelocal known earth field magnitude. If detected, again the gyro will beused for short duration rotation data.

In summary, it is to be appreciated that the two rate sensors discussedabove can overcome the limitation of each individual sensor. Withsufficient processor power, rotation information should be determinedsufficiently to provide for the seamless for long term, highly accurateinertial motion capture.

Alternative Applications

The present invention has been disclosed in conjunction with numerousapplications. While these applications are illustrative of preferredembodiments, they nevertheless are merely indicative of suitableapplications, and are not to be considered as the only applicationswherein the present invention may be used. Moreover, the probableapplications for this present invention include, without limitations,golf, baseball (bat and pitching hand), tennis hockey, fly-fishing orany type of “ball and stick” sport. Note that not all applicationsrequire the full sensor array. If the singularity issue is not importantrelative to using the magnetometers as a differential rate sensor, the 3gyro sensors can be left off. This is particularly true in applicationswhere it is unlikely that there will be magnetic distortion issues suchas in baseball, wooden or aluminum bats, carbon fiber tennis rackets,etc.

If the three gyros are not included in a particular embodiment, thesystem becomes much cheaper, lighter and smaller. Additionally, if themotion being measured is fast where no real-time bio-feedback will beemployed, only post-analysis, the magnetometer singularity becomes moot.Curve fitting with pre and post singularity data will allow a very goodextrapolation to the lost data. Using only pre-singularity data asneeded in the real-time application will not be as good as a fit.

Data Synchronization

In order to compare measured motion data to known motion data, here aretwo types of data synchronization needed for the real-time bio-feedbackapplication.

Single Variable

Single variable analysis is the simplest which is attempting to synch asingle particular motion attribute with respect to time. A referencemotion error file will be generated from the reference motion filestored in flash and transferred to the FRAM circular buffer, which isnot used during the real-time bio-feedback mode. The FRAM is used as aconvenient temporary storage for comparison to the incoming data sampleby sample.

As an example, assume we are trying to compare angular position .vs.time to generate an error signal. The reference motion file data mustcalculate the angular position from the data as this parameter is notpart of the raw data. Once calculated, a 1×N array is created in theFRAM with the 1^(st) entry being the synchronization trigger. Bypre-calculating the reference values prior to the application, thereal-time processing burden is reduced by a factor of two.

Further processing reduction can be realized by “normalizing” the storeddata to the current temperature of the IMMCAP module prior to comparisonto the current motion data. In this way, the real-time IMMCAP sensordata stream does not have to be temperature compensated as the storedreference data has already been adjusted in non-real-time.

With this approach, the processor merely has to calculate the parametervalue from the data stream in real-time. Once the parameter iscalculated, it is compared to the 1^(st) entry in the FRAM 1×N array.Sequential samples will be compared to the 1^(st) entry UNTIL a matchoccurs. Once the match occurs, the index into the 1×N FRAM array isincremented for each subsequent comparison to the M+1 real-time datastream.

Each comparison will result in an error value based on the difference inthe Nth FRAM array entry to the Mth real-time data value. An actualerror tone will be generated based on this error and other parameterssuch as sensitivity. This will continue until the end-of-record isreached in the FRAM buffer.

Additional speed can be realized by moving blocks for the FRAM N×1 arrayinto local SRAM. It is unclear if this would be required but is apossibility.

Multiple Variable

In this mode, more than one motion parameter is being compared withrespect to time. As an example, we could try to compare angular velocityand angular position at the same time with respect to time. In this typeof application, we would need to create a 2×N array with two calculatedentries from the reference motion file, i.e. angular position andangular velocity, for each time Nth increment.

As the real-time data is received, the Mth angular velocity and angularposition is calculated. Depending on which parameter is used forsynchronization, this parameter is used to compare to the 1^(st) entryin the FRAM 2×N array, most likely the angular position in this case.

Once synched, the generation of the error tone will have to bedetermined via a chosen algorithm which would weight the two errorsources and generate the appropriate error tone. With a simple twovariable example, we could generate two independent error tones, leftear for position and the right ear for velocity.

Flexible Circuits

Depending on the application, either flexible or rigid circuit boardsmay be used. In either case, the components will be potted and mostlikely have a mechanical low pass filter, i.e. some kind of foam aroundthe parts to make it robust against dropping on a hard surface.

Calibration

The initial accelerometer, magnetometer, and gyro sensitivity and offsetcan be determined and stored in non-volatile memory at the time ofmanufacture. Coefficients for temperature compensation can also bestored at this time. Due to the mature nature of the magnetometer andaccelerometer sensors, it is unlikely that further calibration will beneeded once in use. However, the current state of the MEMS gyros willmost likely require frequent calibration to prevent excessiveintegration errors as previously discussed due to offset drift.

The current gyro offsets can be determined by a “calibration” mode thatis executed on the start of any application. By placing the IMMCAPmodule in a motionless state, the uncertainty of the initial gyrooffsets, i.e. sensor output with no rotation, can be greatly reduced byaveraging multiple measurements over a fixed period with the offsetuncertainty reduced by the square root of the number of samples

Additionally, the magnetometers can dynamically determine the offsetdrift of the gyros with time and temperature as well as sensitivitychanges. The magnetometers can also extend the signal range of the gyrosas well. The gyros have a +/−150 degree/sec signal limit, this can beextended up to about 600 deg/sec but a limit exists. If the rotationrate exceeds this limit, the output saturates and is not useful. Themagnetometers acting as a differential rate sensor have no such limitand can kick in if the output of the gyroscopes saturate thereby losingaccuracy in their signal simply by providing the addition digital signalprocessing required to extract the rate information from the real-timemagnetometer data stream.

It is also to be appreciated that the IMMCAP may be formed into a 3Dprinted circuit board rectangular (“Borg” cube) in form. The physicalconfiguration for the 3D (Borg) cube is quite unique as well, as theindividual panels of the 3D cube is assembled in a flat form.Construction of the 3D cube (Borg cube) is similar to a box—having a boxbottom, east and west side, north and south side with the box topattached to the north side. The IC's and some of the passive componentsare mounted on the up side of the flattened box. The majority of thepassives components are on the down side of the box. Once the box isfolded, the up side of the flattened box becomes the inside of a 3D cubewith approx 65% of the internal volume taken up by the IC's and passiveswith the bottom becoming the outside of the 3D cube.

This unique configuration allows the entire 3D cube to be approximately19 mm×17 mm×9 mm in size. This size is considerably smaller than othermotion sensors currently available.

Due to the possibility of high frequency vibrations which might beimparted to the IMMCAP module through striking objects with the devicesbeing measured, it may be advantageous to securely fix the motionsensing components within the IMMCAP module. For example, the componentswithin the module may be potted to provide the most robust sensor,minimizing errors and structural damage during periods of highacceleration. Also, it is important to realize that many high frequencycomponents of signals from IMMCAP sensors will be successfully filteredfrom the lower frequency signal by the application of low-pass filtersto the outputs of the sensor leads.

Design Variations

Depending on the particular application of the present invention, threedesigns are contemplated. When there is no magnetic interference, i.e.no external ferromagnetic material near enough to cause a disruption inthe local earth field, the accel/magnetometer is the configuration ofchoice if the singularity is not a issue or it can be resolvedmathematically in two applications. First of all, the resolution can bedone in real-time via a forward extrapolation from previous data toreplace the singularity with limited but acceptable accuracy.

If magnetic disturbances are to be expected, the accel/magnetometer/gyroconfiguration is desirable. The gyro data can be used during the periodsof the mathematical singularity and/or detected magnetic interference.By using the gyro intermittently, the accumulation of error due to noisecan be minimized. Recall that the magnetometer used as a differentialrate sensor has approx 13 bits of resolution while the best resolutionthe gyro can produce is about 8 bits with a 10 Hz bandwidth. If thestart orientation is known and high magnetic interference is expected,the magnetometer is not needed if the gyro accuracy is acceptable whenused stand-alone.

In a preferred embodiment, the system of the present invention willcontain all three sensor types with the processor located elsewherebeing smart enough to know when to switch from the magnetometer ratesensor to the gyro. This is easily detected as any magnetic interferencefrom external ferromagnetic material will almost always result in thesuperposition resultant magnetic field vector to increase beyond that ofthe earth field alone as well as change the direction of the resultantvector

While the particular tri-axial rate and position sensing motion capturesystem as herein shown and disclosed in detail is fully capable ofobtaining the objects and providing the advantages herein before stated,it is to be understood that it is merely illustrative of the presentlypreferred embodiments of the invention and that no limitations areintended to the details of construction or design herein shown otherthan as described in the appended claims.

1. A motion sensing system, comprising: one or more motion sensors, eachmotion sensor operable to measure data on motion and orientation of themotion sensor and comprising (1) a microprocessor to process andtransform measured data into digital sensor data and (2) a sensorcommunication interface to output the digital sensor data; and acontroller, separate from and external to the one or more motion sensorsand the microprocessor in each of the one or more motion sensors,comprising (1) a controller communication interface in communicationwith the one or more motion sensors via the sensor communicationinterface and (2) a controller memory to receive the digital sensor datafrom the one or more motion sensors, wherein the controller processes,in real time as the digital sensor data is being received, the receiveddigital sensor data to produce a measured motion profile of the one ormore motion sensors and to compare the measured motion profile to areference motion profile for the one or more motion sensors that isstored in the controller microprocessor, and wherein the controllerproduces an indicator signal to indicate a deviation of the measuredmotion profile from the reference motion profile.
 2. The system as inclaim 1, wherein: the sensor communication interface in each motionsensor is an RF interface that transmits a wireless RF signal carryingthe digital sensor data, and the controller communication interface isan RF interface that wirelessly transmits and receives data.
 3. Thesystem as in claim 1, wherein: each motion sensor comprises a tri-axialmagnetometer to measure a local magnetic field vector at each motionsensor, and wherein the system comprises a mechanism to process measureddata on the local magnetic field to measure a differential rate ofrotation of each motion sensor relative to a local earth magnetic fieldvector.
 4. The system as in claim 1, comprises: an alert mechanism thatresponds to the indicator signal to produce an alert signal to alert aperson of the deviation of the measured motion profile from thereference motion profile when the deviation exceeds a tolerance range.5. The system as in claim 1, wherein the controller comprises acommunication link to send out the digital sensor data for furtheranalysis and processing.
 6. The system as in claim 1, comprising: a bodysuit structured to be complaint and to hold a plurality of groups of themotion sensors and the controller, wherein the groups of the motionsensors are located on selected portions of the body suit correspondingto selected rigid body segments, respectively, and each group of themotion sensors acquires motion data of a respective selected rigid bodysegment and communicates the acquired motion data to the controllerwhich assemblies the acquired motion data from the groups of the motionsensors to provide motion data for analysis of body motion.
 7. Thesystem as in claim 1, comprising: a shaft mounted appliance modulestructured to engage to a golf club and to hold a motion sensor whichmeasures the motion of the golf club caused by a person to produce themeasured motion profile of the golf club, wherein the reference motionprofile includes one or more reference golf club swings for golftraining, wherein the sensor communication interface in each motionsensor is an RF interface that transmits a wireless RF signal carryingthe digital sensor data, and the controller communication interface isan RF interface that wirelessly transmits and receives data.
 8. Thesystem as in claim 3, wherein: each motion sensor comprises a tri-axialgyroscope to measure a rate of rotation of each motion sensor inaddition to the measured differential rate of rotation from thetri-axial magnetometer, and wherein the system comprises a mechanism touse the measured differential rate of rotation from the tri-axialmagnetometer to indicate a rotation rate of the motion sensor when theexternal earth magnetic field is not aligned with any one of threeorthogonal axes of the tri-axial magnetometer and to select the measuredrate of rotation from the tri-axial gyroscope when data when theexternal earth magnetic field is aligned with one of three orthogonalaxes of the tri-axial magnetometer.
 9. The system as in claim 3,wherein: each motion sensor does not include a tri-axial gyroscope tomeasure a rate of rotation of each motion sensor, and wherein the systemcomprises a mechanism to: use data samples of the measured differentialrate of rotation from the tri-axial magnetometer to estimate a rate ofrotation of the motion sensor during a period when the external earthmagnetic field is not aligned with any one of three orthogonal axes ofthe tri-axial magnetometer.
 10. The system as in claim 4, wherein thealert signal is an acoustic, optical or tactical feedback signal. 11.The system as in claim 6, wherein: each motion sensor comprises atri-axial magnetometer to measure a local magnetic field vector at eachmotion sensor, and wherein the system comprises a mechanism to processmeasured data on the local magnetic field to measure a differential rateof rotation of each motion sensor relative to a local earth magneticfield vector.
 12. The system as in claim 7, wherein the motion sensor isan integrated sensor module that comprises a battery power supply tosupply power for operating the motion sensor.
 13. The system as in claim7, wherein the motion sensor is a microelectromechanical system (MEMS)motion sensor.
 14. The system as in claim 7, comprising: an alertmechanism that responds to the indicator signal to produce an alertsignal to alert a person of the deviation of the measured motion profilefrom the reference motion profile when the deviation exceeds a tolerancerange.
 15. The system as in claim 9, comprising: a shaft mountedappliance module structured to engage to a golf club and to hold amotion sensor which measures the motion of the golf club caused by aperson to produce the measured motion profile of the golf club, whereinthe sensor communication interface in each motion sensor is an RFinterface that transmits a wireless RF signal carrying the digitalsensor data, and the controller communication interface is an RFinterface that wirelessly transmits and receives data.
 16. The system asin claim 11, comprising: a mechanism that uses data samples of themeasured differential rate of rotation from the tri-axial magnetometerto estimate a rate of rotation of the motion sensor during a period whenthe external earth magnetic field is not aligned with any one of threeorthogonal axes of the tri-axial magnetometer.
 17. The system as inclaim 11, wherein: each motion sensor comprises a tri-axial gyroscope tomeasure a rate of rotation of each motion sensor in addition to themeasured differential rate of rotation from the tri-axial magnetometer,and wherein the system comprises a mechanism that uses the measureddifferential rate of rotation from the tri-axial magnetometer toindicate a rotation rate of the motion sensor when the external earthmagnetic field is not aligned with any one of three orthogonal axes ofthe tri-axial magnetometer and to select the measured rate of rotationfrom the tri-axial gyroscope when data when the external earth magneticfield is aligned with one of three orthogonal axes of the tri-axialmagnetometer.
 18. The system as in claim 15, wherein the motion sensoris a microelectromechanical system (MEMS) motion sensor.
 19. A motionsensing system, comprising: one or more motion sensors, each motionsensor operable to measure data on motion and orientation of the motionsensor and comprising (1) a microprocessor to process and transformmeasured data into digital sensor data and (2) a sensor communicationinterface to output the digital sensor data; and a controller comprising(1) a controller communication interface in communication with each ofthe one or more motion sensors via the sensor communication interfaceand (2) a controller memory to receive the digital sensor data from theone or more motion sensors, wherein the controller processes, in realtime as the digital sensor data is being received, the received digitalsensor data to produce a measured motion profile of the one or moremotion sensors and to compare the measured motion profile to a referencemotion profile for the one or more motion sensors that is stored in thecontroller microprocessor, and wherein the controller produces anindicator signal to indicate a deviation of the measured motion profilefrom the reference motion profile; and a body suit structured to becomplaint and to hold a plurality of groups of the motion sensors andthe controller, wherein the groups of the motion sensors are located onselected portions of the body suit corresponding to selected rigid bodysegments, respectively, and each group of the motion sensors acquiresmotion data of a respective selected rigid body segment and communicatesthe acquired motion data to the controller which assemblies the acquiredmotion data from the groups of the motion sensors to provide motion datafor analysis of body motion, and wherein: each motion sensor is amicroelectromechanical system (MEMS) motion sensor.
 20. The system as inclaim 19, wherein: each MEMS motion sensor includes a tri-axial MEMSaccelerometer; a tri-axial MEMS gyroscope and a tri-axial MEMSmagnetometer.
 21. The system as in claim 19, wherein: the sensorcommunication interface in each motion sensor is an RF interface thattransmits a wireless RF signal carrying the digital sensor data, and thecontroller communication interface is an RF interface that wirelesslytransmits and receives data.
 22. The system as in claim 19, wherein thecontroller communication interface is connected to each of the motionsensors to communicate with each motion sensor via the sensorcommunication interface.